Internal combustion engines such as those found in cars and trucks may produce combustion byproducts and/or products of incomplete combustion which may be in the engine exhaust and emitted into the environment. Per emissions regulations, the exhaust may be treated to reduce the concentration of such products and, therefore, reduce pollution. Although spark ignition (i.e., gasoline) engines may use three-way catalytic converters to satisfy emissions regulations, compression ignition (i.e., diesel) engines typically employ two-way catalytic converters which may not efficiently reduce nitrogen oxides (NOx). Accordingly, diesel engines may include selective catalytic reduction (SCR) systems in order to seek reduction in nitrogen oxide concentrations. Improving performance of such systems remains an ongoing area of research and development.